A runners for a Francis turbine comprises a crown, band and plurality of turbine blades extending between the crown and the band. During manufacture, the blades are usually fastened to the crown and band by welds. When the diameter of the runner starts to exceed 5 meters, for example, it is known to split the turbine runner into two segments divided from each other by a plane passing along the axis of the runner so as to permit the runner to be transported from the manufacturing site to the dam site. This radial plane cuts through the crown, the band and portions of some of the blades.
At the dam site, the split runner segments are assembled by making welding joints at the crown, the band and the split blades. The welding of the blades requires great care due the stresses that are to be placed on the blades during turbine operation. These weld joints are typically made with a filler metal base material of CA-6NM which is an iron-chromium-nickel-molybdenum alloy that is hardened by post weld heat treatment. During post weld heat treatment, the weld joints are susceptible to cracking which requires reprocessing of the welded joint until no cracks in the joints are present.
Accordingly any improvement in manufacture of the split runner for a Francis type turbine that does not lead to weld joints in the runner blades and the potential cracking of the blade joints during a post weld heat treatment would be advantageous.